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Aircraft Engines
' As an ASDL student, you have access to the ASDL network. Be sure to upload this article to the internal wiki before the due date or it may not be graded. See William Engler if you have any questions.' The question being answered is: What are typical types of aircraft engines used? Introduction An aircraft engine is the propulsion system for an aircraft. Different propulsion systems develop thrust in different ways, but the principle is based on Newton's third law of motion. In any propulsion system a working fluid is accelerated by the system and a reaction to this acceleration produces force('' in this case thrust'') on the system. Thrust is the force which moves an aircraft forward through the air. Types of Aircraft Engines All aircraft engines operate by compressing outside air, mixing it with fuel, burning the mixture, and extracting energy from the resulting high pressure hot gases. Different types of aircraft engines are: #Reciprocating engine/propeller/Piston-prop #Turbojet #Turbofan #Turboprop Reciprocating engine/propeller/Piston-prop The piston-prop was the first form of aircraft propulsion. This type of engine consists of a piston-cylinder arrangement. This type of engine operates on four basic strokes. Intake, Compression, Compression and Exhaust. During Intake, air-fuel mixture is taken into the cylinder, then it is compressed to raise the pressure during compression stroke. The compressed air-fuel mixture is then ignited to produce tremendous power due to expansion of gases leading to a power stroke. The hot gases are then pushed out of the cylinder during exhaust stroke and then the cycle repeats. Piston engines drive a propeller via a spinning shaft producing the required force/thrust. Piston Engine arrangement: The pistons can be arranged in four ways: radial, in-line, oppositional and "V." Turbojet A turbojet engine contains diffuser, compressor, burner, turbine and nozzle. Flow enters the inlet diffuser with free stream velocity. In the diffuser the air is slowed, with the consequent increase in pressure and temperature. It then enters the compressor, where the work is done on the air by the rotating compressor blades, hence greatly increasing pressure and temperature. After discharge from the compressor, the air enters the combustor, where it is mixed with fuel and burned at essentially constant pressure. The burned fuel air mixture then expands through a turbine which extracts work from the gas. The turbine is connected to the compressor by a shaft, and the work extracted from the turbine is transmitted via the shaft to operate the compressor. Finally, the gas expands through a nozzle and is exhausted into the air with the exit jet velocity producing the forward thrust. Turbofan The turbojet engine forms the core of a turbofan. However in a turbofan engine, the turbine drives not only the compressor, but also a large fan external to the core. The flow itself is contained in a shroud that is wrapped around the core. The flow through turbofan engine is split into two paths. One passes through the fan and flows externally over the core and the second passes through the core itself. This ratio of the air passing externally over the core to that of the air passing through the core is called the bypass ratio. Bypass ratio ranges from as high as 6 to as low as 0.25. Turboprop In its simplest form, a turboprop consists of an intake, compressor, combustor, turbine and a propelling nozzle. Air is drawn into the intake and compressed by the compressor. Fuel is then added to the compressed air in the combustor, where the fuel-air mixture then combusts. The hot combustion gases expand through the turbine. Some of the power generated by the turbine is used to drive the compressor. The rest is transmitted through the reduction gearing to the propeller. Further expansion of the gases occurs in the propelling nozzle, where the gases exhaust to atmospheric pressure. The propelling nozzle provides a relatively small proportion of the thrust generated by a turboprop.